1. Field of the Invention
The invention relates to a vehicle, an abnormality determination method for an internal combustion engine, and an abnormality determination device for an internal combustion engine, and more particularly to a technique for changing an operation region that determines an abnormality according to the atmospheric pressure.
2. Description of Related Art
An internal combustion engine is available in which fuel is burned in cylinders. In the internal combustion engine, the fuel is not necessarily always burned normally. For this reason, a variety of abnormality determination functions are incorporated in a control device that controls the internal combustion engine.
Japanese Patent Application Publication No. 9-96243 (JP-A-9-96243) discloses a misfire detection device for an internal combustion engine that determines a misfire detection region by the engine load state and detects a misfire state within the misfire detection region.
Where a wide detection region is set, an abnormality can be determined in the operation state in which an abnormality can be easily detected erroneously. For this reason, the abnormality detection accuracy can degrade. Therefore, it is desirable that the detection region be restricted. However, when the detection region is restricted, the frequency of the internal combustion engine being operated in an operation state outside the detection region may increase. For example, where an internal combustion engine is operated under a higher revolution speed and a lower load as the atmospheric pressure decreases with the object of ensuring a negative pressure inside the intake pipe, the internal combustion engine can operate in an operation state outside the detection region restricted so as to include the operation state (load and revolution speed of output shaft) corresponding to the normal atmospheric pressure. In a case like that, abnormality detection may not be accomplished even if there is engine abnormally.